There are numerous hand devices for extruding paste- or cream-like food substances, such as the common "bakers sleeve" or the plunger devices of the type shown in U.S. Pat. No. 1,996,628. There are hand-operated devices using a rotating drive screw in a piston to push a similar substance out of an extruding sleeve, such as the one shown in U.S. Pat. No. 2,420,616. There are devices, such as the one shown in U.S. Pat. No. 3,984,033, which use an electric motor connected to a household electrical outlet to rotate a drive screw in one direction, to move a nonrotating piston along an extruding sleeve so as to push out the substance to be extruded, and in an opposite direction to return the piston to its home position. And, there are devices such as those shown in U.S. Pat. Nos. 1,466,509 and RE 26,180, which use a nonrotating drive screw driven forwardly, along an extruding sleeve, to push the substance to be extruded out by a piston, or backwardly, to bring the piston back to its home position. The nonrotating drive screw is driven along the sleeve axis by a rotating gear wheel having an internal thread meshing with the external thread of the drive screw. While it is desirable to have powered extruding devices, such as those shown in the three last cited patents, particularly in the case of substances such as dough which requires substantial pressure for adequate extrusion, and it is desirable that such devices be portable, for home use, such as the devices shown in U.S. Pat. Nos. 3,984,033 and RE 26,180, it is also desirable that such portable devices be convenient to use and be simple and inexpensive so that they can find widespread use in the home. It is also desirable that such powered device be safe to the user and that they not expose the user to electrical shock even when used impoperly. It is also desirable that such devices be easily disassembled for cleaning and again assembled for using, and that they be simple to operate. It is believed that none of the known devices of this kind meets all of these desirable goals, and this invention is directed to providing a different device of this type which better meets these goals.
A device embodying the invention is battery-operated, so as to completely avoid the possibility of dangerous electrical shock to a user, it is simply and inexpensively made, primarily of molded plastic components, so as to be inexpensive, and is simple to operate and to disassemble for cleaning and again assemble for use. More specifically, a device embodying the invention includes a plastic tube and a plastic pusher which fits closly within the tube but can move along the tube axis. The tube and the pusher have cooperating means for preventing relative rotation between the two about the tube axis. For example, the tube is generally cylindrical but has two flattened sides and the pusher is similarly shaped. The back end of the tube is detachably secured to a housing molded of plastic mateial, e.g., by screwing the back end of the tube into the housing. The housing includes a rotatable gear wheel having a central, internally threaded opening coaxial with the tube axis. A drive screw extends through this internally threaded opening of the gear wheel and through suitable openings in the housing, and the back end of the tube is secured detachably to the pusher such that it cannot rotate with respect to it; for example, the pusher has at its back side a square opening which receives a square front end of the drive screw. The drive screw has a back portion which is externally threaded, to mesh with the internal thread of the gear wheel, and a reduced diameter front portion which passes through the threaded opening of the gear wheel without engaging the thread. The housing also contains an electrical motor for rotating the gear wheel about the tube axis through a suitable power transmission device, such as a gearing connecting the motor shaft to the gear wheel. The motor is connected to batteries through a suitable electrical switch.
In typical operation, the tube is attached to the housing, the pusher is moved all the way back in the tube to its home position and the tube is filled with the food substance to be extruded. A selected extruding disc or an extruding tip is placed at the open front end of the tube and secured in place by screwing on a tube cap. The drive screw is put in place from the back of the housing by moving its reduced diameter front end through the internally threaded opening of the gear wheel until the threads of the drive screw and the gear wheel engage. At that time the motor is turned on while holding the drive screw to keep it from rotating. The drive screw is moved forwardly along the tube axis by the motor so that its reduced diameter front end can engage nonrotatably with the pusher. At this time there is no longer a need to hold the drive screw to keep it from rotating, and continuing operation of the motor drives the drive screw forwardly and thus moves the pusher forwardly to extrude the substance through the extruding disc or tip. The threaded portion of the drive screw runs out of the drive wheel just before the pusher reaches the end of the tube. To refill or clean the extruder, the tube is unscrewed from the housing and the drive screw, which has run forwardly out of the gear wheel, is removed from the back of the tube. The tube cap and the extruding disc or tip is removed from the front end of the tube and the pusher is pushed back to its home position and the tube refilled. For cleaning, the pusher is pushed forwardly out of the tube.
The drive screw never enters the substance being extruded, and this keeps the drive screw threads and the gear wheel driving it along the tube axis clean and at a low coefficient of friction as compared with, for example, the device of U.S. Pat. No. 3,984,033, cited above, where the drive screw extends into the substance being extruded and that substance can foul the meshing threads of the drive screw and piston. Moreover, the thread of the drive screw on this invention is interrupted by cutouts extending along the length of the drive screw, which cutouts do not interfere with the smooth operation of the invented device but reduce substantially the cross-sectional area and thickness of the drive screw and thereby reduce the time it takes to mold the drive screw of a thermoplastic material and the amount of material needed. It is noted that such cutouts are possible in the arrangement of this invention, where the drive screw does not enter the substance being extruded, but would not be possible in an arrangement such as in U.S. Pat. No. 3,984,033, cited above, because the substance being extruded would back-leak through the space between the cutouts and the internally threaded central opening of the piston.